1. Field of the Invention
The present invention relates to a conveying apparatus provided with a continuous conveying control for a sheet.
2. Description of the Related Art
In an image printing apparatus or an image reading apparatus, a conveying apparatus provided with a feeding portion for feeding sheets one by one into the apparatus from a sheet stocking portion, a conveying portion for conveying the fed sheets to a printing region or a reading region, and a discharge portion for discharging the sheets for which printing or reading has finished is provided. The feeding portion, the conveying portion, and the discharge portion are arranged on a series of paths so that transfer of the sheets among them is performed continuously and processing such as printing or reading is executed without delay.
Many of such conveying apparatuses are provided with a continuous-conveying control configuration for performing discharge of a previous page and feeding of a subsequent page in an interlocking manner for efficient processing of a plurality of sheets. Japanese Patent Laid-Open No. 4-148756 discloses, for example, a conveying control method such that a sensor for detecting a rear end portion of a sheet is arranged on a conveying path of the sheets and the subsequent page is fed at the time when the rear end of the previous page is detected.
With the configuration in which the sensor is arranged on the conveying path as in Japanese Patent Laid-Open No. 4-148756, if slip occurs between the sheet and a conveying roller, for example, the sensor cannot detect the rear end of the sheet forever. Thus, in order to detect such a state as an error, such control is executed that means for measuring a rotation amount of the conveying roller is provided, and if the sensor does not detect the rear end of the sheet even after the conveying roller has been rotated by a predetermined amount, it is determined to be a conveying error. At this time, it is only necessary that the predetermined amount is a sufficient amount to discharge the sheet during processing. In the case of an apparatus for executing processing for sheets with various sizes, the above-described predetermined amount can be set in accordance with the sheet having the largest length among the sheet sizes that can be processed. However, in this case, even if the size of the sheet is small, error determination cannot be made unless the conveying roller is driven by an amount more than necessary and larger than an appropriate conveyed amount for the sheet concerned. That is, even if the continuous-feeding control configuration is provided, long time is consumed for the error determination, and efficient continuous-feeding control cannot be made.